Ilona staggered across road first perhaps (7)
I believe the answer is:
ordinal
'first perhaps' is the definition.
(first is a kind of ordinal)
'ilona staggered across road' is the wordplay.
'staggered' indicates an anagram.
'across' means one lot of letters goes inside another.
'road' becomes 'rd' (abbreviation).
'ilona' is an anagram of 'oinal'.
'oinal' placed around 'rd' is 'ORDINAL'.
(Other definitions for ordinal that I've seen before include "Number such as first or second" , "Numerals such as first and second" , "First, for One" , "Ranking number" , "For example, first" .)